Portable electronic devices such as cellular phones having RFID wireless tags have come into widespread use in recent years, and some of which include antenna coils for wireless tags as described in, for example, Patent Document 1. FIG. 17 is a perspective view illustrating the principal part of a portable electronic device 800 shown in Patent Document 1. FIG. 17 illustrates the structure of the portable electronic device 800 including a substrate 500 and a cylindrical antenna coil 600 having a magnetic core 601 disposed on the substrate 500. The antenna coil 600 is disposed such that the axial direction thereof is parallel to the surface of the substrate 500, and can be interlinked with a magnetic flux parallel to the surface of the substrate 500.
Moreover, Patent Document 2 shown in FIG. 18 discloses a portable electronic device 810 capable of being interlinked with a magnetic flux parallel to the surface of a substrate 510 in all directions by disposing an antenna coil 610 including an L-shaped magnetic core 611 formed of a first leg portion 611a and a second leg portion 611b on the substrate 510.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-16409
Patent Document 2: Japanese Unexamined Patent Application Publication No. 10-242742
FIG. 19 is a schematic view illustrating an example of magnetic-flux paths when the portable electronic device 800 shown in FIG. 17 is held over a RFID reader/writer. In FIG. 19, reference symbol φ denotes a magnetic flux generated by the reader/writer. As shown in FIG. 19, the portable electronic device 800 is usually held over the reader/writer such that the principal surface of a metallic casing 700 of the portable electronic device 800 is parallel to the principal surface of the reader/writer.
However, magnetic-shielding objects such as the metallic casing 700 are located between the antenna coil 600 and the reader/writer in the structure shown in Patent Document 1, and the magnetic flux is blocked by the metallic casing 700. Therefore, almost no magnetic flux passes through the antenna coil. Furthermore, the axial direction of the magnetic core 601 of the antenna coil 600 is parallel to the surface of the substrate 500. Therefore, the antenna coil 600 cannot be interlinked with the magnetic flux generated by the reader/writer (magnetic flux orthogonal to the axial direction of the antenna coil 600), and cannot communicate with the reader/writer.
Similarly, almost no magnetic flux orthogonal to the axial directions of the magnetic core 611 passes through the antenna coil 610 shown in Patent Document 2 since the magnetic flux is blocked by the substrate and the metallic casing. The antenna coil 610 has a portion without a coil at a position where the first leg portion 611a and the second leg portion 611b of the L-shaped magnetic core 611 intersect each other at a right angle, and can be interlinked with the magnetic flux orthogonal to the axial directions at the intersecting portion. However, the magnetic resistance at end surfaces of the magnetic core 611 is large since the antenna coil 610 is disposed in the central area of the substrate. This prevents the magnetic flux from being guided into the antenna coil 610. That is, the antenna coil 610 described in Patent Document 2 also cannot be interlinked with the magnetic flux generated by the reader/writer (magnetic flux orthogonal to the axial directions of the magnetic core 611), and cannot communicate with the reader/writer.